Give units a bit of a cleanup:
Give units a bit of a cleanup:

1) Fix a bug where the recursion on prefixes where if recusrion failed
	then the next attempt started too far along the string.
2) Up some internal limits that we were about to hit off.
3) Change the constness and signedness of some things and complete missing
	prototypes.
4) Remove the readerror function 'cos it could print out the wrong
	wrong file name. Replace it with more useful error messages.
5) Use sizeof when passing buffers to fgets.
6) Warn about empty prefix definitions.

Reviewed by:	iedowse

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